The present inventions relates to a chromatography technology such as a liquid chromatography technology, and particularly to a data processing method.
In chromatographs such as a liquid chromatographic analyzers a gas chromatographic analyzer or the like a sample to be measured is left to pass through a column to be separated into components and each of the separated components is detected as an output value at each elapsing time using a photometer such as a chromatographic detector.
Signals output from the chromatographic detector are recorded as time sequential data having a time interval of several hundreds ms. This is what is called a chromatogram having signal intensity in the ordinate and retention time in abscissa. In general, the signal intensity is converted to a digital value Ij every an arbitrary time interval (time tj) to execute data processing.
FIG. 3 shows an example of a chromatogram obtained by executing a body fluid amino acid analysis.
As shown in FIG. 3, peaks of 11 components from Gly (glycine) to Tyr (tyrosine) densely exist in the range of retention time from 23 to 34 (min). In such a case, area-quantitative calculation is conventionally executed using a vertically dividing method in which a vertical line is drawn from each minimum point between peaks, that is, what is called xe2x80x9ca rootxe2x80x9d. However, this method produces an error as large as several tens % to cause an incorrect result when the peaks are strongly overlapped with each other. Therefore, when the chromatogram of such a kind needs to be quantitatively analyzed in a high accuracy it has been general that the analyzing time is lengthened to improve the separation degree.
On the other hand, in order to perform quantitative calculation without lengthening the analyzing time even if peaks are overlapped so strongly with each other, quantitative calculation is tried to be performed using numerical analysis in a manner like data processing. This method is, for example, a non-linear least square method.
In the case of using the nonlinear least-square method, at least three independent parameters (A: area, TR: retention time, "sgr": standard deviation) are used as variables in order to execute fitting of a peak for one component. Therefore, in order to execute fitting of peaks for a plurality of components, it is necessary to calculate three parameters of Ai, TRi, "sgr"i for each of the components (i).
The conventional examples of using the non-linear least-square method are disclosed in Japanese Patent Application Laid-Open No. 6-324029 and Japanese Patent Application Laid-Open No. 63-151851.
These examples disclose that overlapping peaks on a chromatogram are curve-fit using a waveform function such as the Gaussian function or an EMG function (exponentially modified Gaussian function) which can express an asymmetric waveform of a peak. As shown in these examples, the overlapping peaks can be separated into individual peak waveforms, and the quantitative calculation can be performed by obtaining peak sizes such as a peak area and so on corresponding to a component of each of the peaks.
However, in the conventional examples using the non-linear least-square method, the separation of the peak waveforms is applied to two or three overlapping peaks, but not applied to more than three overlapping peaks.
The reason is that in the case of separating the overlapping peak waveforms using curve fitting through the non-linear least-square method, as the number of peak components is increased to 3, 4, 5 . . . , there occurs a phenomenon that the fitting processing is difficult to be converged or that the separation of peaks can not correctly performed (the error is increased).
For example, in the case of the chromatogram shown in FIG. 3, when fitting is tried to the 11 components from Gly to Tyr at a time, the 33 parameters of 11xc3x973 must be determined at a time. This is very difficult calculation processing to the non-linear least-square method, and accordingly various kinds of techniques are necessary in order to solve this problem. Therefore, when the, curve-fitting is executed using the non-linear least-square method in the case of existing many overlapping peaks on a chromatogram, a measuring operator must specify calculation regions (time windows) for 2 or 3 peaks seeming to be converged one by one. This process expenses much time and much effort, and in addition, there is a problem in the reliability of the calculation result because the regions are artificially determined.
An object of the present invention is to provide a chromatographic analyzer capable of easily executing curve fitting using the non-linear least-square method to a chromatogram having a plurality of overlapping peaks.
The present invention to attain the above object is characterized by a chromatographic data processor for executing data processing of a chromatogram obtained by separating a sample to be measured using a column and detecting the separated sample, wherein fitting processing is executed to each peak in an arbitrary time region having the plurality of peaks of the chromatogram starting from the front side of the time region or from the back side of the time region, and the processed peaks are subtracted from the time region of the chromatogram so that the plurality of peaks in the chromatogram can be separated from one another.
The object, the operation and the effect of the present invention will be described in detail in the section of DESCRIPTION OF THE PREFERRED EMBODIMENTS to be described later.